A 6-year-old child who regularly consumes unpasteurized cow's milk presents with chronic mesenteric lymphadenitis. The isolate is dysgonic (sparse growth), niacin negative, and identified as Mycobacterium bovis. While designing the treatment regimen, which first-line drug must be omitted?
- A Rifampicin
- B Isoniazid
- C Pyrazinamide ✓
- D Ethambutol
Correct answer: C. Pyrazinamide
Explanation
M. bovis is naturally, uniformly resistant to pyrazinamide because its pncA-encoded pyrazinamidase does not convert the drug to active pyrazinoic acid, so pyrazinamide adds nothing to the regimen. M. bovis remains susceptible to isoniazid, rifampicin and ethambutol. Dysgonic growth and negative niacin test distinguish it from the eugonic, strongly niacin-positive human tubercle bacillus.
Reference: Jawetz, Melnick and Adelberg's Medical Microbiology, 28th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.